SUMMARY IRBP is expressed much earlier than needed for any putative role in the visual cycle. In the previous grant cycle, we showed that IRBP is needed in early retina development, as without it we detected morphological changes coincident with terminal differentiation of rods and cones, and precocious development of the outer plexiform layer. At the same time, we discovered excessive eye growth and elongation of the optical axis starting distinctly at P7. This implies a role for IRBP in controlling eye growth even without vision-based signaling. We now know that IRBP loss causes diverse and severe eye diseases including profound myopia and retinal degeneration, and we recently discovered sluggish pupillary light reflexes (PLRs). In recent human GWAS studies, IRBP polymorphisms are associated with refractive error and corneal curvature. Previous linkage studies established that IRBP defects caused combined RP and severe myopia. We view abnormalities of IRBP deficiency in the context of eye disease that affect normal determination of eye size, based on strong and abundant previous and concurrent work in developmental biology of the Drosophila eye and organ size fate. We test the same five principal pathways that regulate size determination in the IRBP knockout eye. We seek to understand posited hierarchical relationships among myopia, RD, and other abnormalities in IRBP mutations. To do that we have constructed and validated a new conditional knockout (KO) mouse and a new traditional KO. Here we use them to sort out the temporal, spatial, and mechanistic relationships that cause these three major symptoms. Last, we test efficacy of drugs known to slow myopia or organ size, in the IRBP-/- model asking if they are effective in reducing any or all IRBP deficiency symptoms.